医学寄生虫学：Hookworm 钩虫

1、Hookworm 钩虫BriefMembers of family Ancylostomidae are commonly known as hookworms.They live in their hosts intestine, attaching to the mucosa and feeding on blood and tissue fluids sucked from it.cause hookworm disease (Ancylostomiasis)The most significant risk of hookworm infection is anemia, second

2、ary to loss of iron (and protein) in the gut.Hookworm infects approximately a fifth of the worlds population and is the 2nd most common human helminthic infection. Hookworms parasitize more than 900 million people worldwide and cause daily blood loss of 7 million liters. Species of HookwormHuman hoo

3、kworms: 1) Ancylostoma duodenale (十二指肠钩口线虫, 十二指肠钩虫) 2) Necator americanus (美洲板口线虫, 美洲钩虫）Animal hookworms: 1) Ancylostoma ceylanicum (锡兰钩口线虫) 2) Ancylostoma caninum (犬钩口线虫) 3) Ancylostoma braziliense (巴西钩口线虫) (caused cutaneous larval migrans)Africa, India, China, South East AsiaBrazil, USA(Texas), Af

4、rica, India, China ,South East AsiaMorphology Adult Small nematodes (1-1.5 cm)The anterior end is curved dorsally, giving the worm a hook like appearance.The buccal capsule is large and carries characteristic teeth (Ancylostoma) or plates (Necator)The posterior end of the male worm is elaborated int

5、o a copulatory bursaA. duodenale and N.americanus Morphologyegg57-76 m 35-47 moval-roundthin and colorless shellclear space between the egg-shell and the ovum. One ovum in the fresh egg but 2 to 8 cells in constipated (便秘） stoolsrhabditiform larvae and filariform larvaeThe rhabditiform larvae (free-

6、living stage) that emerge feed on bacteria and organic debris, molt twice, and develop into slender, infective filariform larvae in 5 to 8 days.Third stage larva (filariform larva) is the infective form. It is slender and measures 0.50.7 0.025 mm. The mouth is closed, oesophagus is present in the an

7、terior third of the body. The tail is pointed. filariform larva of hookworm (from Parasite image library of CDC, USA) Infective larva of Necator americanusHookworm rhabditiform larva Thermotaxis30min to 1hHyaluronidase透明质酸酶collagenase 胶原酶During the last molt, the cuticle is retained and encloses the

8、 larva as a sheath.infective larvae (filariform)life cycle adultsExternal environmentIn human bodyfilariform（infective stage）5-6daysFree livingrhabditiform larvae（diagnostic stage）With fecesTempera25-30 moisture 60-80%1-3 days eggMate and produce eggsSwall-owedPenetrate skin vesseles, lymphaticsRigh

9、t heartlungbronchustracheapharynx(intestine) Route of infection1）Skin 2）Oral mucosa（A. doudenale)3）Placenta 4）Mothers milk5）Paratenic hosts（ A. doudenale can be transmitted through ingestion of undercooked meat,including beef, lamb, pork,rabbit )Key points of life cycleSite of inhabitation: small in

10、testine of humanFood: blood and tissue fluidInf. Route: by skinDiagnostic stage：eggs； filariform larvaeInf. Stage: Larva 3 or filariform larvaeLife span: Ad 15years, Na 3-7yearsPathogenesis stage：adults、filariform larvaeBlood-lung migration: skin, cavum, right heart, lungsPathogenesisLarva: the inva

11、sion and migration phasecutaneous phase: hookworm dermatitis（钩蚴性皮炎）pulmonary phase:Adult: the intestinal phaseGastrointestinal symptom: pica（异嗜症） geophagy anemia（贫血）iron deficiency anemiaPathogenesis1.1 hookworm dermatitis 2wCaused by penetration by the filariform larvae Itching and a rash at the si

12、te of entry Skin penetration and associated secondary bacterial infection can result in “ground itch” allergic skin reaction intense itching Pathogenesis1.2 Pulmonary phase usually asymptomatic During this phase, there may be a brief period of cough, fever, expectoration, sputum with blood, Large nu

13、mbers of larvae migrating through the lungs at the same time may cause pneumonitis, asthmaworms attach to the mucosa and feed on blood Pathogenesis1.3 Gastrointestinal symptom Attachment of adult worms and injury to upper intestinal mucosa Anorexia, epigastric pain, nausea, vomiting, diarrhea, and g

14、astro-intestinal hemorrhagePica（异嗜症）: loss of normal appetite and desire to eat soil (geophagy 异嗜症) or un-normal materials Pathogenesis-AnemiaWorms attach to the intestine mucosa by the buccal capsule and feed on the mucosa they cause a considerable amount of blood loss. 1) ingests mucosal tissue wi

15、th blood 2) much of the blood is then excreted into intestine lumen 3)blood also is lost by seepage around the attachment site. 4) old wound attachment sites oozes blood for several days. 5) anti-coagulant secreted also contributes to blood loss.0.1ml (N.a.) to 0.26 ml (A.d) per worm, up to 200 ml p

16、er day in heavy infectionsInfections with A. duodenale are considered more pathogenic than N. americanus infections. Intestinal hemorrhagePathogenesis1.4 anemia -Chronic heavy infection microcytic hypochromic anemia 低色素小细胞型贫血 anemia with microcytes that are hypochromic (reduced in size and in hemogl

17、obin content); the most common type is iron deficiency anemia symptom：Fatigue, weakness, Dizziness, Skin pallor, Pale conjunctiva, Dyspnea, palpitations，heavy infections: hypoproteinemia血液蛋白不足, hepatosplenomegalyAtrophic glossitis and koilonychias (nail deformities) Atrophic glossitis in a patient w

18、ith severe microcytic hypochronic anemia due to heavy hookworm infection. The tongue is smooth and lacks papillae. Severe hookworm anemia in the same patient showing nail deformities (koilonychias). In this condition, the nails become thin and concave with raised edges. potbelly in children and with

19、 delayed puberty, mental dullness, heart failure and death.in the young, often causes stunted growth and below-average intelligence.Pregnant woman:Pregnancy-induced hypertension syndromeAbortion, premature delivery, stillbirtheosinophilia（嗜酸性粒细胞增多症） is variable, more than 15%, up to 70%PathogenesisD

20、iagnosisDirect microscopic examination : based on finding of the characteristic eggLarval cultivation(钩蚴培养法) :based on finding of hatched larvae, must be differentiated from those of strongyloides. (Hookworm larva have a much longer oral opening than that of Strongyloides larva ) EpedemiologyHookwor

21、m occurs worldwide N. americanus found mainly in the Americas and Australia A. duodenale found mainly in Middle East, North Africa and Southern Europe Both species are found in Asia, the Americas and AfricaGlobal distribution of hookworm in 2003 Epedemiologyinfection rate1979 56%；1995 18%;2005 6.12%

22、In china194 million people are infected with hookworms in ChinaN. americanes is most common in south of China. A.duodenale is most common in north of China （1）Source of infection：human（patient、carrier） worm： Ad. 20,000egg/worm/day Na. 10,000egg/worm/day （2）Route of transmission Warmer and poor sanit

23、ation Inadequate disposal of feces Using nightsoil as fertilizer Bare-foot walking （3）susceptible population countryurban； adultchildren Occupation: Miners and peasants who plant coffee, vegetable, sweet-potato, corn (dry-plants)EpidemiologyAppropriate temperatureHigh moisture Poor sanitationmineAnc

24、ylostoma was found throughout mines in Europe (at the turn of 19th century, severe hookworm disease was an official occupational hazard in German coal mines eligible for workmans compensation)Prevention and Treatmenttreatment of infected persons Albendazole:肠虫清single oral dose of 400 mg to adults, 200 mg to children